The present invention is directed toward apparatus for handling coils of sheet metal strip which includes apparatus for unwinding a coil of single metal strip for slitting to form a plurality of separate strips of predetermined width for rewinding the strips into individual coils and, more particularly, toward a vertical accumulator that maintains continuous tension in each strip during the rewinding operation.
In the continuous production of rolling of metal strip, it is difficult to prevent the forming rolls of a rolling mill from bowing by a slight amount. This is particularly true with wider strips which is caused, in part by the weight of the forming rolls, but primarily by the enormous radial loading on the rolls as they progressively compress the metal strip to reduce its thickness. As a result, the metal strip which is formed usually varies in cross-sectional thickness with the center portion of the strip being a few thousandths of an inch thicker than the edge portions. Furthermore, as the strips increase in width, usually the differential in thickness across each strip also increases. Thus when the single strip is coiled, the center portion of the single strip has a tendency to increase in diameter at a faster rate than the edge portions which results in producing greater tension in the center portion of the strip within the coil.
When the original single coiled strip is subsequently run through a slitting operation to form a plurality of separate metal strips, it has been found that the stresses within the original strip are relieved, and in addition, the strips formed from the center portion of the single strip will have a slightly greater thickness than those strips formed from the edge portion. Thus when each of these separate strips is rewound on a common mandrel into separate coils, the tension in the strips forming the center coils of the mandrel is substantially greater than the tension in the strips forming the outer or end coils.
As is well known in the art, is desirable to maintain sufficient tension in each of the strips forming the separate coils during the rewinding operation so that the coils are not loosely formed and will not collapse or telescope after they are removed from the rewinding mandrel. Thus a common procedure is to provide a frictional resistance or drag on each of the separate strips between the slitting and rewinding operations. This drag develops a progressively increasing slack in the strips formed from the edge portions of the original single strip. To accommodate the slack, it is common to form a large deep pit in line between the slitting and rewind operation in which to suspended loops of the strips as the slack progressively increases. The pit essentially acts as an accumulator for the suspended loops between the slitting and rewinding operations.
In view of the trend toward larger coil diameters for obtaining more efficient handling of the strips and more efficient use of the machines which subsequently receive the metal strips, it has been found necessary to construct deeper and deeper pits. Pits may be as deep as twenty or thirty feet or more. Since the coils being unwound, slit and rewound and the equipment for performing these operations are extremely heavy, the entire operation is normally performed on the ground floor of a facility and on a solid concrete slab. Thus, when a pit is needed, it must be dug down through the concrete and into the earth below. The pit itself must then be finished with a concrete floor and walls and the like to prevent ground water or the like from seeping in. Depending on the terrain, it may or may not be possible to dig and properly finish the necessary pit. But even when it can be done, it is obviously an expensive process. Furthermore, once the pit is formed, its depth cannot be changed without going through additional substantial expense.
Therefore, a need exists for a less expensive accumulator that does not require the construction of a large pit between the slitting and rewinding operations and which can be used in substantially any facility.